For demodulating an OFDM (Orthogonal Frequency Division Multiplex) signal typified by MMAC (Multimedia Mobile Access Communication), it is first necessary to determine the position of a known symbol (preamble) contained in a received signal. It should be noted that the known symbol is a symbol added intending synchronization, estimation of a channel position, and the like.
There is a method which uses correlation to determine the position of the known symbol in the received signal. The method is described below. First, the FFT (Fast Fourier Transform) is applied to the received signal. The FFT is applied to the known symbol, and then, the resulting symbol is converted to the conjugate complex. Then, there is determined a product of a result of the application of the FFT to the received signal and a result of the conversion to the conjugate complex of the result of the application of the FFT to the known symbol. The inverse FFT (IFFT) is applied to the product to determine a correlation. This correlation is a function of time, and time at which the correlation takes the maximum value is estimated as the position of the known symbol.
However, it is necessary for fast Fourier transform to digitally represent the signal. Thus, the position of the known symbol cannot be estimated more precisely than a sampling interval used for converting the analog signal to the digital signal.
An object of the present invention is to highly precisely estimate the position of a specific pattern such as the known symbol in a signal such as the OFDM signal.